This invention relates to warning lights such as those used on emergency vehicles to alert others as to the presence of the emergency vehicle. More particularly, the present invention relates to the heat dissipation from the power supply used to operate such lights.
The warning lights may be of conventional design, including strobe lights and halogen lights, or they may be configured in an array of light emitting diode""s (LED""s) that are used to generate light which, when appropriately directed, has a relatively high intensity. When the LED""s of such arrays are energized simultaneously and intermittently, the resulting bursts of light function as effective warning devices for primary emergency vehicles such as fire, rescue, towing, DOT and ambulances as well as other vehicles.
The dissipation of heat from warning lights and the power supplies for such lights must be carefully controlled because the warning lights as well as other solid-state electronic devices used in such assemblies are susceptible to thermal damage. The possibility of damage resulting from overheating is also increased when devices are closely spaced in an array to achieve the illusion of a single source of light. The present invention is focused on the dissipation of heat from the power supply employed for vehicular warning light assemblies. The dissipation of heat from the power supply is a component of the overall design parameters relating to heat dissipation throughout the entire warning light assembly.
The prior art to which the invention relates includes U.S. Pat. No. 5,016,139 entitled xe2x80x9cElectronic Power Supply with Enhanced Heat Transfer Characteristicsxe2x80x9d, issued to James L. Stopa and Stephen C. Bibbiani and assigned to the assignee of the present invention. This patent discloses an electronic power supply, which employs energy storage capacitors in an enclosure defining a housing including a base and a cover. The capacitors are resiliently supported within the enclosure on a carrier. Integral receivers extend from the underside of a top cover that are registered with the carrier and engage the capacitors to clamp the capacitors in a fixed position within the housing. The housing exterior includes a thermal radiator comprising multiple fins, which extend outwardly for dissipating heat generated in the capacitors.
The present invention has particular utility in electronic systems that supply power to intermittently operated loads and especially to high intensity light generator loads and has applicability to a wide range of power supplies. A number of electronic power supplies are commercially available that are suitable for use with gas discharge tubes for warning light systems. For example, U.S. Pat. Nos. 4,013,921 and 4,321,507 generally disclose power supply circuitry of the type for which the present invention is applicable. These power supplies employ one or more relatively large electrolytic capacitors which are discharged to flash tubes to provide the power for generating the requisite light output.
Typically, power supply circuitry of the type to which the invention relates is housed in an enclosure which is at least in part defined by a metal or plastic box. The components, which supply the power to the flash tube(s) and/or light emitting diode arrays, occupy a substantial space within the enclosure and, as noted above, generate a significant quantity of heat during the operation of the power supply. The significant heat generated by the components presents a problem in terms of efficiently positioning and mounting the components within the enclosure and for transferring the heat from the vicinity of the components to prevent overheating which could damage or affect the operation of the power supply and/or the arrays of lights.
An object of the present invention is to provide a power supply for a warning light which is constructed to dissipate a substantial amount of heat and which occupies a relatively small volume.
Another object of the present invention is to provide a compact power supply having an efficient and relatively low cost construction wherein the power supply has the capability of effectively dissipating a substantial amount of heat from the assembly.
A further object of the present invention is to provide a power supply for a vehicular emergency light bar which effectively functions as a structural support module and an effective dissipate of heat.
It has now been found that these and other objects of the invention may be attained in a power supply for a light bar assembly for use as a warning light on an associated emergency vehicle. The power supply has a generally planar printed circuit board mounting at least one discrete component which generates a significant amount of heat. A housing surrounds the printed circuit board and includes a generally planar heat sink plate that is disposed in generally parallel relationship to the generally planar printed circuit board. The generally planar heat sink plate is disposed in thermal conduction relationship with respect to the one discrete component and a fastener extends through the discrete component to urge the printed circuit board and the generally planar member together.
In some forms of the invention, the housing has laterally extending feet and a material may be disposed between the discrete component and the generally planar heat sink plate to improve thermal conduction therebetween. Various forms of the invention may have a threaded fastener extending through the discrete component which may be a MOSFET.